The Deep Subseafloor Biosphere

Recent discoveries indicate that microbes beneath the Earth’s surface make up as much as half of all living material on our planet. One habitat for subsurface microorganisms is the volcanic rock that forms the ocean basins. These rocks cover at least fifty percent of the Earth’s surface and are the most abundant rock types on Earth. Low temperature (<100°C) hydrothermal ocean fluids circulate everywhere within these porous and permeable volcanic rocks, creating temperatures and chemical gradients that form plausible habitats for a variety of microorganisms. In fact, there is growing evidence that indigenous communities of microbes extend throughout the immense volume of aging basement rocks underlying the global system of mid-ocean ridge flanks and ocean basins, making the volcanic rocks of the ocean basins the largest habitat on Earth.

From 2008 to 2014, our deep subsurface microbiology team has repeatedly sampled basalt-hosted, deep subseafloor crustal fluids from boreholes drilled along the Juan de Fuca Ridge flank in the Northeast Pacific Ocean using pumps and samplers capable of collecting whole water and filtered particulates in situ. The instrumented boreholes, sitting at 2600 m depth, penetrate ~100 to 260 m of bottom sediments and another ~48 to 300 m of igneous basement where they tap into hot (up to 65°C), anoxic fluid within Earth’s largest deep subsurface aquifer. As part of the Department of Energy Joint Genome Institute’s 2016 Community Sequencing Program, we are collaborating with Olivia Nigro and Grieg Steward to sequence metagenomes, metatranscriptomes, and single cell genomes from environmental samples collected from crustal fluids of the Juan de Fuca Ridge flank.